Joints



March 16, 1965 F. Z1MMER ETAL. 3,173,522

JOINTs Filed Nov. l5, 1961 2 Sheehs-Sheel'l l a fl Inventors FRANTISEKZlmM EK PETER )maar ,MARSHALL March 16, 1965 F. zlMMER ETAL 3,173,522

JoINTs Filed Nov. 15, 1961 2 sheets-sheet 2 P .5 kv

/g 6 6) III l; 7 i 7 I s 555A A n venlorS By (NCTM/4% Attorneyr UnitedStates Patent Ollce 3,l73,522 Patented Mar. 16, 1965 3,173,522 JOINTSFrantisek Zimmer, 49a Ave. Winston Churchill, Brussels, y Belgium, andPeter Robert Marshall, 48 Malcolm Road,

Shirley, England Filed Nov. 15, 1961, Ser. No. 152,575 8 Claims. (Cl.189-36) This invention relates to joints of the kind which are subjectto such changes in temperature that there is difliculty in maintainingan effective joint, particularly against fluids under pressure, by theusual mechanical means such, for example, as bolts or other clampingmeans, in association wth packing washers or the like.

In the case of a simple joint comprising two llanged members (formingpart of a duid-containing structure subject to severe changes intemperature) which are secured together by the tightening of nuts orbolts which pass through the flanges, the flanged members are usuallyheated or cooled more rapidly than the bolts. Measurements have shownthat the maximum difference in temperature between the ilanged membersand the bolts can range from about 10 C. to about 100 C. depending interalia upon the severity of the heating or cooling. This difference in thetemperature produces a differential expansion or contraction between thebolts and the flanged members which can adversely affect the tightnessof the joint. In some constructions which we have studied a dilierenceof 10 C. produced a differential tension in the bolts of 2.3 kg. per sq.mm., i.e., 23 kg. per sq. mm. for a difference of 100 C. j

The differential tension can, in the case of rapid heating, increase thetension of the bolts to such an extent that the elastic limit isexceeded; thus a permanent plastic elongation of the bolts is producedwith the resultant probability of the joint not being leak proof.

In the case of rapid cooling the bolts usually remain for a time hotterthanthe flanged membersV and under such circumstances their tension cantemporarily fall below the value necessary to ensure suflicienttightness to prevent leaks.

It may also be mentioned that leaks, even temporary, between jointsworking at high pressures and high temperatures abrade by erosion andmay entail expensive repairs.

With a view to eliminating the undesirable differences between thetemperatures of the bolts and the llanged elements complicated andcost-ly arrangements are often used. Such a case, for example, is anarrangement used in the construction of steam turbines. It comprisescausing the steam to circulate over the bolts and between the twoflanges of the flanged elements.

The principal object of this invention is to provide means in joints forreducing the tendency to leak arising from temperature changes.

According to the invention means for securing a tightenable jointbetween two members of a structure subject to a temperature differentialon sudden heating or cooling, comprises the interposition between thejointed members of a thermally conductive element manufactured by powdermetallurgy methods and so constructed that it is capable of beingcompressed as the joint is tightened, thereby providing thermal contactbetween the members.

The element is preferably formed from material having a high thermalconductivity. One suitable material is copper, and the necessarycompressibility can be provided by making the element porous by knownpowder metallurgy methods. A preferred porosity is in the region of 23to 35%, the element then having the character of a metallic sponge.

In one form of the invention for use in joints in which members aresecured together by one or more bolts passed through holes in themembers, the holes in the members are of diameter greater than at leasta part of the or each bolt, and this part of the bolt is surrounded byannular thermally conductive elements which on tightening the bolt willbe compressed axially and so caused to expand radially so as to makeintimate contact with the bolt and the walls of the holes. If the shankof the bolt is of diameter smaller than the peak diameter of its screwthreads, the annular elements are formed in halves for fitting aroundthe shank, and can be secured in position for example by wire orcirclips or byr adhesive on their end faces.

In order that the features of the invention may be clearly understoodreference will now be made to the accompanying drawings, in which:

FIGURES l and 2 are fragmentary sectional views of a joint constructedin accordance with the features of the invention, and

FIGURE 3 is an end elevation of one of the annular powered metal bushesof FIGURES 1 and 2;

FIGURE 3A is a side elevation of the bush of FIG- URE 3;

FIGURE 4 is an end elevation of one ofthe steel bushes of FIGURES l and2; and

FIGURE 4A is a side elevation of bush of FIGURE 4.

As shown in FIGURES l and 2, the two flanged members l and 2 of a jointare bolted together by bolts 3 each having a shank 4 of diameter smallerthan the peak diameter of the threaded ends, the holes 5 in the flangesbeing of diameter somewhat greater than the screw threaded ends. Anumber of annular bushes 6, preferably fabricated of porous copper,formed in halves by powder metallurgy, as shown in FIGURE 3, are mountedside-by-side on the stem or shank 4 of each bolt and secured in positioneither by circlips fitted in circumferential grooves 7 formed in theouter surfaces of the bush halves, or in the arrangement shown inFIGURES l and 2 by contact adhesive on their end faces which se-A curesthe two halves of each bush together as soon as they are brought intocontact. Similar steel bushes 8 also formed in halves, as shown inFIGURE 4, are mounted on the shank 4 at each end or" the pack of copperbushes 6, and the bores of these steel bushes are shaped to fit thatportion of the shank which increases in diameter towards the threadedends of the bolt 3. A steel sleeve 9 is fitted over the screw threadedends of the bolt 3 so as to engage the steel bush 8 and a nut 10 bywhich the bolt is tightened. The external diameter of the copper andsteel bushes 6 and 8 and the sleeves 9 is such as to slide easilythrough the holes 5 in the flanges 1 and 2. The bolt, with the bushesand sleeve assembled, as shown in FIGURE 1, is passed through the holesS in the flanges. With the nuts l0 fitted and tightened, as shown inFIGURE 2, the sleeve 9 transmit axial pressure to the bushes 6 and 8 asthe nuts are tightened, compressing the copper bushes 6 and causing theminitially to expand radially so as to make intimate contact with thebolt shank 4 and the walls of the holes 5. After such radial expansionthe bushes 6 are compressed axially in bulk to enable the flanges 1 and2 to be tightened together in sealing relation.

When the joint is tightened, the copper bushes, being in intimatecontact with the flanges and the bolt, transmit rapidly to the bolts alltemperature changes in the llanges, so that differential expansion ofthe flanges and bolts is substantially reduced, and the above-mentioneddifliculties produced by such differential expansion are avoided.

In order to assist the sliding of the bushes on the bolt and in theholes as they are axially compressed, the bolt and the holes arepreferably lubricated on assembly by dipping or painting with lubricant,forexample colloidal graphite or molybdenum 'disulphide Thebushesthemselves may alternatively be dipped orY painted with lubri#y cant, ormaybe impregnated with lubricant during manu' facture.

In a test on the cover plate of heat exchanger,V the coverwas securedwith'bolts fitted with bushes accord-p ing to the invention andwithnormal bolts.'V One of each Vof these bolts was drilled with .anarrow axial hole in which a thermocouple was fitted, and a similar holewas drilled in the platemidway between the two test bolts, f

for a third thermocouple; The bolts were of diameter 38.1 min. and ofstem diameter 3l mm. and length 185 mm. Eightfporous'copper bushes,formed in halves, of

inner diameter 28 mm. outer diameter 4l mm. and porosityr29.5% (i.e.,29.5% by volume of air in the material) were itted over the boltsaccording to the invention. On tightening the bolts the pack of busheswasreduced in length, by 185mm. (i.e., one tenth'of its length). v

The temperature ofthe. assembly was allowed to come'Y to equilibrium at310' C. by admitting Vsuperheated'V steam, and cold water was thenadmitted 'to Vcool to a temperature ofV 240 C. f The temperaturesrecorded by the thermocouples were noted during thiscooling, when it wasfound that the temperature of the bolt fitted Vwith bushes according tothe invention followed closely the temperature of the cover whereas thetemperature of the normal bolt differedV from that of the coverthroughout' the cooling by up to 19 C.

By virtue of the invention not onlyareleakage andV Y bolt, and #thereVVbeing vforce transmitting means between the risk of fracture orstretching of bolts due `to excessive Y forces. avoided, but also as aresult of this the frequentV j retightening of the bolts and the riskofover-straining them are substantially reduced and thus `the time inwhich piant is likely to be out of commission for maintenance isreduced.r Furthermore, since the forces on the bolts Y and the anges arereduced, somewhat smaller bolts VVand anges may in some circumstances beused, leading to reduced costs.Y

We claim:

1. In a joint between two members of a structure subject to suddentemperature changes and comprising iianges on` said members securedtogether by bolts Vpassing through aligned boresV in the. flanges,annular bushing means of compressible high thermal conductivity metalsurrounding 4each of said bolts ,within said bores, and

means for tightening said bolts'tourge said anges tightly Y together,`said tightening means axially'compressing andV radially expanding saidVbushing means into intimate heat exchange contact with its associatedbore and bolt.

VsteelV force transmitting annulusaxially interposed between the nut andthe adjacent end of said bushing means within the adjacent bore. z

Y 5. In a joint between twomembers of a structure subject to suddentemperature Vchanges and comprising :flanges on said members securedjtogether by bolts passing through alignedrbores in the. anges, bushingmeans comprising a plurality of jannularbushings disposed side by sidealong eachbolt Within the associated bores, each ofsaid bushings beingof compressible metalV having high thermal conductivity, andmeansrreactingbetween oppositezendso'the bolts for tensioning the boltsto draw said flanges tightly together, saidftightening means beingeffective toaxially compress said bushing means whereby said annular,bushingsV are compressed axially in abutting relation andexpanded'radi'ally into'intimate heat exchange contact with theassociated boreV andboit.

6. In 4the joint definedfin claim 5, said annularbush- VingsV eachconsisting diametrally split halves of porous powdered sintered metal. Yn Y 7. In Ythe joint defined in claim` 5,: each bolt havingenlargedendmernberthereon outside the flanges, one 0f said enlarged Vendmembers being a nut threaded on the said nut and the adjacent end ofsaid bushing means within therbore comprising axially rigid annularmeans.

. n 8.' 'In the Vjoint deined in claim?, said bolt having areduced'diameter shank on Ywhich saidlbushing means is mounted, and saidaxiallyV rigid ymeans comprising a rigidmetal bushing within the boreabutting the end rof the bushing means, "and a rigid metal sleevesuxroundingthe threaded end of the bolt axially interposed betweensaidnut` and said rigid bushing. f Y l j l References Cktedin the file ofthis patent c UNITED sTATEsPATENTs 1,257,943 Y Howard c Feb.26, '19181,937,465V Sherwood Nov. 28, 1933 V2,000,653 Wilkinson May'7,`rl9352,196,683 Pickstone Apr. 9, 1940I 2,808,616 g, VBaldasarre et-al Oct. 8,41957 3,045,785 l Ferguson July 24, 1962 3,052,452 1962 Y Taga Sept. 4,

1. IN A JOINT BETWEEN TWO MEMBERS OF A STRUCTURE SUBJECT TO SUDDENTEMPERATURE CHANGES AND COMPRISING FLANGES ON SAID MEMBERS SECUREDTOGETHER BY BOLTS PASSING THROUGH ALIGNED BORES IN THE FLANGES, ANNULARBUSHING MEANS OF COMPRESSIBLE HIGH THERMAL CONDUCTIVITY METALSURROUNDING EACH OF SAID BOLTS WITHIN SAID BORES, AND MEANS FORTIGHTENING SAID BOLTS TO URGE SAID FLANGES TIGHTLY TOGETHER, SAIDTIGHTENING MEANS AXIALLY COMPRESSING AND RADIALLY EXPANDING SAID BUSHINGMEANS INTO INTIMATE HEAT EXCHANGE CONTACT WITH ITS ASSOCIATED BORE ABDBOLT.